Construction vehicles, such as backhoe vehicles, are known to use parking brakes. One such configuration is a mechanically actuated brake where the operator uses a lever acting on a cable or pull rod to engage and disengage the parking brake. Engagement occurs when the operator pulls a lever located in the cab of the vehicle. The lever acts on a cable or pull rod. The cable or pull rod engages the parking brake. To disengage the park brake, the lever in the cab is returned to its original position. This type of brake actuation is strictly mechanical. But in certain prior art configurations, a vehicle does not have space available for the lever. This design also requires that the operator remember to pull the lever to engage the parking brake when parking the vehicle. Should the operator forget, the vehicle could roll away, causing a hazardous condition.
Similarly, another prior art configuration is the use of a spring-applied, hydraulically released (SAHR) canister attached to the brake. For this configuration, the parking brake is mounted to the transmission and a SAHR canister is attached to the parking brake. The transmission hydraulic circuit is connected to the canister. Springs in the canister push on a piston which is attached to a pull rod or cable on the brake. If the vehicle is turned off or hydraulic pressure to the canister is interrupted for any reason, the springs push on the piston, the piston pulls the rod or cable, and the rod or cable engages the brake. To release the park brake, the low pressure transmission hydraulic circuit acts on the piston, and the piston compresses the springs that are engaging the brake and thus releases the brake. In order for the park brake to engage once again, hydraulic pressure must fall to zero. A problem with this configuration is that the hydraulic pressure available to certain brakes is very low. In order to overcome the spring force, the piston would need to be very large. Also, the canister might be too large to fit in the vehicle due to neighboring components, hoses, and hydraulic lines. Further, brakes utilizing a canister, or a lever, have increased complexity, which results in increased costs and potential for leaking.
Another prior art configuration is to use a conventional SAHR parking brake. This configuration uses one or more springs to clamp friction discs together to engage the parking brake. The parking brake will release when hydraulic pressure is applied to an annular piston that compresses the springs. When the springs are compressed, the clamp on the friction discs is relieved. The parking brake engages again when hydraulic pressure falls to zero. The problem with this configuration is that the cylindrical piston area needed to overcome the springs is too large for certain brakes. In these brakes, the necessary design size for the brake would have to be too large to fit in certain vehicles due to neighboring components, hoses, and hydraulic lines.
These prior art configurations have an inconvenient or hazardous method of manually disengaging the brake in the event of a hydraulic system failure. In the event the vehicle should require service, and the hydraulic system is not available to generate pressure, there remains a need to safely manually release the brake in the event the vehicle would need to be towed. There also remains a need for a brake that offers one or more improvements over the prior art, such as a more compact design, the inclusion of a manual release capability, and the ability to utilize a low pressure hydraulic circuit.